May 2021 Daily Mail
Shooting infrared light into the ear may prevent one of the most common causes of hearing loss — and even restore hearing that’s been damaged. That’s the thinking behind a new U.S. trial.
Previous research suggests that infrared light can prevent the death of hair cells, which are key to hearing, as well as trigger repair. Now researchers at the University of Miami are assessing the effectiveness of infrared light delivered to the ear in reducing the effects of noise exposure.This is one of the main causes of hearing loss, which around 11 million people in the UK experience to some degree.
Most noise-induced hearing loss (NIHL) is caused by damage to, and the death of, hair cells in the inner ear. The hair cells convert sound vibrations into electrical signals that are relayed along the auditory nerve and into the brain. We are born with a relatively small number of these auditory hair cells — around 15,000 in each ear — and they decline with age, disease and exposure to loud noise. The latter ‘overworks’ the cells, damaging them. Human hair cells don’t grow back, so once killed they are gone for good.
There are currently no treatments for this hearing loss. Some recent research has focused on infrared light, or near-infrared (NIR). It is already used in medicine for wound healing — it’s thought to improve the supply of oxygen-rich blood to the area — and pain relief.
Research has shown that the light can both prevent and heal NIHL. In one of the latest studies, reported in Peer Journal, mice treated with NIR for ten minutes before being exposed to loud noise all experienced less hearing loss than untreated animals. ‘Our results show that a single NIR pre-treatment of at least ten minutes produces significant protection against noise exposure,’ say the researchers from Charite Medical School in Berlin, Germany.
Previous animal research has revealed that NIR can also work as a treatment, significantly reducing the loss of hair cells when given for an hour daily for up to 12 days after noise exposure.
In a study published in the Journal of Biomedical Optics in 2012, rats given the treatment in one ear were found to have more hair cells, and their hearing ability was better after they were exposed to loud noise, compared with the ear not exposed to the light.
Just how light could have such an effect is unclear. One suggestion is that it interacts with a protein called cytochrome c oxidase, which leads to increased production of adenosine triphosphate (ATP) — higher levels of this compound have been shown to both reduce cell death generally, and start the cell repair processes. It also results in a drop in inflammation, which is implicated in hair cell damage caused by noise.
In a clinical trial with 100 healthy people at the University of Miami in the U.S., participants are being exposed to safe levels of noise on four occasions. They will receive infrared therapy for 30 minutes for half the visits, and sham light therapy for the others. Various tests will be carried out to assess the effects of light on the behaviour of hair cells. One will measure otoacoustic emissions — sound caused by the motion of hair cells as they respond to noise. Jaydip Ray, a professor of otology and neurotology at the University of Sheffield, said: ‘Infrared neuromodulation is a very promising and relatively new concept. If successful on a larger scale, this has the exciting possibility of being a major treatment option for hearing loss.’